Hydrogen + Chlorine → Hydrogen chloride
Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
Sodium + Water → Sodium hydroxide + Hydrogen
Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
(i)
(ii)
Name the substance ‘X’ and write its formula.
Write the reaction of the substance ‘X’ named in (i) above with water.
Calcium oxide reacts vigorously with water to form calcium hydroxide (slaked lime).
Therefore, the blue colour of copper sulphate solution fades and green colour appears.
In this reaction, sodium carbonate and calcium chloride exchange ions to form two new compounds. Hence, it is a double displacement reaction.
(i)
(ii)
Sodium (Na) is oxidised as it gains oxygen and oxygen gets reduced.
Copper oxide (CuO) is reduced to copper (Cu) while hydrogen (H2) gets oxidised to water (H2O).
(a) Lead is getting reduced. (b) Carbon dioxide is getting oxidised. (c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(a) and (b)
(a) and (c)
(a), (b) and (c)
all
(a) and (b)
The above reaction is an example of a
combination reaction.
double displacement reaction.
decomposition reaction.
displacement reaction
(d) The given reaction is an example of a displacement reaction.
Hydrogen gas and iron chloride are produced.
Chlorine gas and iron hydroxide are produced.
No reaction takes place.
Iron salt and water are produced.
Hydrogen gas and iron chloride are produced. The reaction is as follows:
Hydrogen gas combines with nitrogen to form ammonia.
Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
Zinc + Silver nitrate → Zinc nitrate + Silver
Aluminium + Copper chloride → Aluminium chloride + Copper
Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
Potassium bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) + Barium bromide(s)
Zinc carbonate (s) → Zinc oxide (s) + Carbon dioxide (g)
Hydrogen (g) + Chlorine (g) → Hydrogen chloride (g)
Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g)
Double displacement reaction
; Decomposition reaction
Combination reaction
Displacement reaction
Example: Mixture of sodium and chlorine to yield table salt
In other words, combination reactions are exothermic.
Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.
For example: In the process of photosynthesis, plants use the energy from the sun to convert carbon dioxide and water to glucose and oxygen.
Decomposition reaction: 
Combination reaction: 
Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Thermal decomposition:
Decomposition by light:
Decomposition by electricity:
where A is more reactive than
B
In a double displacement reaction, two atoms or a group of atoms switch places to form new compounds.
For example: Displacement reaction:
Double displacement reaction:
For example:
In this reaction, calcium carbonate is obtained as a precipitate. Hence, it is a precipitation reaction. Another example of precipitation reaction is:
In this reaction, barium sulphate is obtained as a precipitate.
Oxidation
Reduction
Oxidation is the gain of oxygen.
For example:
(i) 
(ii) 
In equation (i), H2 is oxidized to H2O and in equation (ii), Cu is oxidised to CuO.
Reduction is the loss of oxygen.
For example:
(i) 
(ii) 
In equation (i), CO2 is reduced to CO and in equation (ii), CuO is reduced to Cu.
Corrosion
Rancidity
Corrosion:
For example, iron, in the presence of moisture, reacts with oxygen to form hydrated iron oxide.
This hydrated iron oxide is rust.
Rancidity:
The process of oxidation of fats and oils that can be easily noticed by the change in taste and smell is known as rancidity.
For example, the taste and smell of butter changes when kept for long. Rancidity can be avoided by:
Storing food in air tight containers
Storing food in refrigerators
Adding antioxidants
Storing food in an environment of nitrogen
Let us mark the three test tubes as A, B, and C. A drop of the solution in A is put on the red litmus paper. Same is repeated with solution B and C. If either of them changes colour to blue, then it is basic. Therefore, out of three, one is eliminated. Out of the remaining two, any one can be acidic or neutral. Now a drop of basic solution is mixed with a drop of each of the remaining two solutions separately and then the nature of the drops of the mixtures is checked. If the colour of red litmus turns blue, then the second solution is neutral and if there is no change in colour, then the second solution is acidic. This is because acidic and basic solutions neutralize each other.
Hence, we can distinguish between the three types of solutions.
Take few pieces of zinc granules and add 5 ml of dilute H2SO4. Shake it and pass the gas produced into a soap solution. The bubbles of the soap solution are formed. These soap bubbles contain hydrogen gas.
We can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the soap bubbles.
The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
The reaction is as follows:
Although aqueous solutions of glucose and alcohol contain hydrogen, these cannot dissociate in water to form hydrogen ions. Hence, they do not show acidic character.
Since the process of dissolving an acid in water is exothermic, it is always recommended that acid should be added to water. If it is done the other way, then it is possible that because of the large amount of heat generated, the mixture splashes out and causes burns.
8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?
?
(a) 1 (b) 4 (c) 5 (d) 10
The solution contains
(a) NaCl (b) HCl (c) LiCl (d) KCl
(a) 4 mL (b) 8mL (c) 12 mL (d) 16 mL
Antibiotic
Analgesic
Antacid
Antiseptic
dilute sulphuric acid reacts with zinc granules.
dilute hydrochloric acid reacts with magnesium ribbon.
dilute sulphuric acid reacts with aluminium powder.
dilute hydrochloric acid reacts with iron filings.
Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen
Sulphuric acid + Aluminium → Aluminium sulphate + Hydrogen
Hydrochloric acid + Iron → Ferric chloride + Hydrogen
It will be observed that the bulb glows in the HCl solution and does not glow in the glucose solution.
Result:
HCl dissociates into H+ and Cl− ions. These ions conduct electricity in the solution resulting in the glowing of the bulb. On the other hand, the glucose solution does not dissociate into ions.
Therefore, it does not conduct electricity.
From this activity, it can be concluded that all acids contain hydrogen but not all compounds containing hydrogen are acids.
That is why, though alcohols and glucose contain hydrogen, they are not categorised as acids.
Acids do not show acidic behaviour in the absence of water because the dissociation of hydrogen ions from an acid occurs in the presence of water only. It is the hydrogen ions that are responsible for the acidic behaviour.
strongly alkaline?
strongly acidic?
weakly acidic?
weakly alkaline?
Neutral → Solution D with pH 7
Strongly alkaline → Solution C with pH 11
Strongly acidic → Solution B with pH 1
Weakly acidic → Solution A with pH 4
Weakly alkaline → Solution E with pH 9
The pH can be arranged in the increasing order of the concentration of hydrogen ions as: 11 < 9 < 7 < 4 < 1
Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
Why does this milk take a long time to set as curd?
(b) Since this milk is slightly basic than usual milk, acids produced to set the curd are neutralized by the base. Therefore, it takes a longer time for the curd to set.
For example:
(i)
During indigestion (caused due to the production of excess of hydrochloric acid in the
stomach), we administer an antacid (generally milk of magnesia,
which is basic in nature). The antacid neutralizes the excess of acids and thus gives relief from indigestion.
Washing soda:
It is used in glass, soap, and paper industries.
It is used to remove permanent hardness of water.
Baking soda:
It is used as baking powder. Baking powder is a mixture of baking soda and a mild acid known as tartaric acid. When it is heated or mixed in water, it releases CO2 that makes bread or cake fluffy.
It is used in soda-acid fire extinguishers.
Malleable: Substances that can be beaten into thin sheets are called malleable. For example, most of the metals are malleable.
Ductile: Substances that can be drawn into thin wires are called ductile. For example, most of the metals are ductile.
iron with steam
calcium and potassium with water
MetalIron (II) sulphateCooper (II) sulphateZinc sulphate Silver nitrate
No reaction Displacement
DisplacementNo reaction
C. | No reaction | No reaction | No reaction Displacement |
D. | No reaction | No reaction | No reaction No reaction |
Use the Table above to answer the following questions about metals A, B, C and D.
Which is the most reactive metal?
What would you observe if B is added to a solution of copper (II) sulphate?
Arrange the metals A, B, C and D in the order of decreasing reactivity.
A + FeSO4 → No reaction, i.e., A is less reactive than iron
A + CuSO4 → Displacement, i.e., A is more reactive than copper
B + FeSO4 → Displacement, i.e., B is more reactive than iron
B + ZnSO4 → No reaction, i.e., B is less reactive than zinc
C + FeSO4 → No reaction, i.e., C is less reactive than iron
C + CuSO4 → No reaction, i.e., C is less reactive than copper C + ZnSO4 → No reaction, i.e., C is less reactive than zinc
C + AgNO3 → Displacement, i.e., C is more reactive than silver
D + FeSO4/CuSO4/ZnSO4/AgNO3 → No reaction, i.e., D is less reactive than iron, copper, zinc, and silver
From the above equations, we obtain:
B is the most reactive metal.
If B is added to a solution of copper (II) sulphate, then it would displace copper.
B + CuSO4 → Displacement
The arrangement of the metals in the order of decreasing reactivity is: B > A > C > D
When iron reacts with dilute H2SO4, iron (II) sulphate with the evolution of hydrogen gas is formed.
Show the formation of Na2O and MgO by the transfer of electrons.
What are the ions present in these compounds?
(ii)
(iii) The ions present in Na2O are Na+ and O2− ions and in MgO are Mg2+ and O2− ions.
(i) Mineral (ii) Ore (iii) Gangue
Ore: Minerals from which metals can be extracted profitably are known as ores.
Gangue: The impurities (sand, silt, soil, gravel, etc.) present in the ore are called gangue.
The metals at the bottom of the reactivity series are mostly found in free state. For example: gold, silver, and platinum.
For example, zinc oxide is reduced to metallic zinc by heating with carbon.
Manganese dioxide is reduced to manganese by treating it with aluminium powder. In this case, aluminium displaces manganese from its oxide.
Oxides of more reactive metals are reduced by electrolysis.
Metal ZincMagnesiumCopper Zinc oxide - - -
Magnesium oxide - - - Copper oxide - - -
In which cases will you find displacement reactions taking place?
Metal Zinc Magnesium Copper
Zinc oxide No reaction DisplacementNo reaction Magnesium oxide No reaction No reaction No reaction Copper oxide DisplacementDisplacementNo reaction
NaCl solution and copper metal
MgCl2 solution and aluminium metal
FeSO4 solution and silver metal
AgNO3 solution and copper metal.
(d) AgNO3 solution and copper metal
Applying grease
Applying paint
Applying a coating of zinc
all of the above.
(We can also apply grease and paint to prevent iron from rusting. However, in case of iron frying pan, grease and paint cannot be applied because when the pan will be heated and washed again and again, the coating of grease and paint would get destroyed.)
calcium
carbon
silicon
iron
zinc is costlier than tin.
zinc has a higher melting point than tin.
zinc is more reactive than tin.
zinc is less reactive than tin.
How could you use them to distinguish between samples of metals and non-metals?
Assess the usefulness of these tests in distinguishing between metals and non-metals.
(b) The above tests are useful in distinguishing between metals and non-metals as these are based on the physical properties. No chemical reactions are involved in these tests.
Anode → Impure metal M
Cathode → Thin strip of pure metal M Electrolyte → Solution of salt of the metal M
What will be the action of gas on
dry litmus paper?
moist litmus paper?
Write a balanced chemical equation for the reaction taking place.
(ii) Since the gas is sulphur dioxide (SO2), it turns moist blue litmus paper to red because sulphur dioxide reacts with moisture to form sulphurous acid.
(b)
Oiling, greasing, or painting: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented.
Galvanisation: An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.
Platinum, gold and silver are used to make jewellery.
Sodium, potassium and lithium are stored under oil.
Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Sodium, potassium, and lithium are very reactive metals and react very vigorously with air as well as water. Therefore, they are kept immersed in kerosene oil in order to prevent their contact with air and moisture.
Though aluminium is a highly reactive metal, it is resistant to corrosion. This is because aluminium reacts with oxygen present in air to form a thin layer of aluminium oxide. This oxide layer is very stable and prevents further reaction of aluminium with oxygen. Also, it is light in weight and a good conductor of heat. Hence, it is used to make cooking utensils.
Carbonate and sulphide ores are usually converted into oxides during the process of extraction because metals can be easily extracted from their oxides rather than from their carbonates and sulphides
Metal | Non- metal |
Metals are electropositive. | Non-metals are electronegative. |
They react with oxygen to form basic oxides. | They react with oxygen to form acidic or neutral oxides. |
These have ionic bonds. | These have covalent bonds. |
They react with water to form oxides and hydroxides. SomeThey do not react with water. metals react with cold water, some with hot water, and some with steam.
They react with dilute acids to form a salt and evolve hydrogen gas. However, Cu, Ag, Au, Pt, Hg do not react. | They do not react with dilute acids. These are not capable of replacing hydrogen. |
They react with the salt solution of metals. Depending on their reactivity, displacement reaction can occur. | These react with the salt solution of non-metals. |
They act as reducing agents (as they can easily lose electrons). | These act as oxidising agents (as they can gain electrons). |
That is why copper is used to make hot water tanks, and not steel.
(ii)
(iii)
Catenation − It is the ability to form bonds with other atoms of carbon.
Tetravalency − With the valency of four, carbon is capable of bonding with four other atoms.
Ethanoic acid (ii) Bromopentane*
Butanone (iv) Hexanal
Answer: *Are structural isomers possible for bromopentane? (i)
There are many structural isomers possible for bromopentane. Among them, the structures of three isomers are given.
, 
 |
(ii)
(iii)
Methanal (formaldehyde)
Hexyne
Alcohols, on the other hand, do not react with carbonates and hydrogen carbonates.
6 covalent bonds.
7 covalent bonds.
8 covalent bonds.
9 covalent bonds.
carboxylic acid.
aldehyde.
ketone.
alcohol.
the food is not cooked completely.
the fuel is not burning completely.
the fuel is wet.
the fuel is burning completely.
Here, carbon requires 4 electrons to complete its octet, while each hydrogen atom requires one electron to complete its duplet. Also, chlorine requires an electron to complete the octet.
Therefore, all of these share the electrons and as a result, carbon forms 3 bonds with hydrogen and one with chlorine.
ethanoic acid.
H2S.
propanone.
F2.
H2 S
Propanone
F2
For example, methane, ethane, propane, butane, etc. are all part of the alkane homologous series. The general formula of this series is CnH2n+2.
Methane CH4 Ethane CH3CH3
Propane CH3CH2CH3 Butane CH3CH2CH2CH3
It can be noticed that there is a difference of −CH2 unit between each successive compound.
Ethanol is a liquid at room temperature with a pleasant odour while ethanoic acid has vinegar-like smell. The melting point of ethanoic acid is 17°C. This is below room temperature and hence, it freezes during winters.
Ethanoic acid reacts with metal carbonates and metal hydrogencarbonates to form salt, water, and carbon dioxide gas while ethanol does not react with them.
For example,
For example,
Micelle formation does not occur in alcohol because the alkyl chain of soap becomes soluble in alcohol.
This reaction is applied in the hydrogenation of vegetables oils, which contain long chains of unsaturated carbons.
The dirt present on clothes is organic in nature and insoluble in water. Therefore, it cannot be removed by only washing with water. When soap is dissolved in water, its hydrophobic ends attach themselves to the dirt and remove it from the cloth. Then, the molecules of soap arrange themselves in micelle formation and trap the dirt at the centre of the cluster. These micelles remain suspended in the water. Hence, the dust particles are easily rinsed away by water.
Autotrophic nutrition | Heterotrophic nutrition |
(i) Food is synthesised from simple inorganic raw materials such as CO2and water. | (i) Food is obtained directly or indirectly from autotrophs. This food is broken down with the help of enzymes. |
(ii) Presence of green pigment (chlorophyll) is necessary. | (ii) No pigment is required in this type of nutrition. |
(iii)Food is generally prepared during day time. | (iii)Food can be prepared at all times. |
All green plants and some bacteria have(iv)All animals and fungi have this type of nutrition. this type of nutrition.
The raw material CO2 enters from the atmosphere through stomata.
Water is absorbed from the soil by the plant roots.
Sunlight, an important component to manufacture food, is absorbed by the chlorophyll and other green parts of the plants.
Enlarged view of a villus
In yeast and human muscle cells, the breakdown of pyruvate occurs in the absence of oxygen whereas in mitochondria, the breakdown of pyruvate occurs in the presence of oxygen.
Since haemoglobin pigment has less affinity for CO2, CO2 is mainly transported in the dissolved form. This de-oxygenated blood gives CO2 to lung alveoli and takes O2 in return.
Transportation of O2 and CO2 in blood
Each lung contains 300-350 million alveoli. These numerous alveoli increase the surface area for gaseous exchange making the process of respiration more efficient.
Heart pumps oxygenated blood throughout the body. It receives deoxygenated blood from the various body parts and sends this impure blood to the lungs for oxygenation.
Being a fluid connective tissue, blood helps in the transport of oxygen, nutrients, CO2, and nitrogenous wastes.
The blood vessels (arteries, veins, and capillaries) carry blood either away from the heart to various organs or from various organs back to the heart.
Thus, it is necessary for them to separate oxygenated and de-oxygenated blood, so that their circulatory system is more efficient and can maintain their constant body temperature.
Components of xylem tissue
Phloem transports food materials from the leaves to different parts of the plant body. The transportation of food in phloem is achieved by utilizing energy from ATP. As a result of this, the osmotic pressure in the tissue increases causing water to move into it. This pressure moves the material in the phloem to the tissues which have less pressure. This is helpful in moving materials according to the needs of the plant. For example, the food material, such as sucrose, is transported into the phloem tissue using ATP energy.
Components of phloem tissue
Structure of a nephron Functioning of a nephron:
The blood enters the kidney through the renal artery, which branches into many capillaries
associated with glomerulus.
The water and solute are transferred to the nephron at Bowman’s capsule. In the 
proximal tubule, some substances such as amino acids, glucose, and salts are
selectively reabsorbed and unwanted molecules are added in the urine.
The filtrate then moves down into the loop of Henle, where more water is absorbed.
From here, the filtrate moves upwards into the distal tubule and finally to the collecting duct.
Collecting duct collects urine from many nephrons.
The urine formed in each kidney enters a long tube called ureter. From ureter, it gets transported to the urinary bladder and then into the urethra.
nutrition.
respiration.
excretion.
transportation.
(c) In human beings, the kidneys are a part of the system for excretion.
transport of water.
transport of food.
transport of amino acids.
transport of oxygen.
In a plant, the xylem is responsible for transport of water.
carbon dioxide and water.
chlorophyll.
sunlight.
all of the above.
cytoplasm.
mitochondria.
chloroplast.
nucleus.
Aerobic respiration | Anaerobic respiration |
1.It occurs in the presence of O2. | 1.It occurs in the absence of O2. |
2.It involves the exchange of gases between the organism and the outside environment. | 2.Exchange of gases is absent. |
3.It occurs in cytoplasm and mitochondria. | 3.It occurs only in cytoplasm. |
4.It always releases CO2 and H2O. | 4.End products vary. |
5.It yields 36 ATPs. | 5.It yields only 2 ATPs. |
Anaerobic respiration occurs in the roots of some waterlogged plants, some parasitic worms, animal muscles, and some micro-organisms such as yeasts.
Alveoli and capillaries
Flow of blood in the heart:
The heart has superior and inferior vena cava, which carries de-oxygenated blood from the upper and lower regions of the body respectively and supplies this de-oxygenated blood to the right atrium of the heart.
Flow of blood in the human heart
The right atrium then contracts and passes the de-oxygenated blood to the right ventricle, through an auriculo-ventricular aperture.
Then the right ventricle contracts and passes the de-oxygenated blood into the two pulmonary arteries, which pumps it to the lungs where the blood becomes oxygenated. From the lungs, the pulmonary veins transport the oxygenated blood to the left atrium of the heart. Then the
left atrium contracts and through the auriculo-ventricular aperture, the oxygenated blood enters the left ventricle.
The blood passes to aorta from the left ventricle. The aorta gives rise to many arteries that distribute the oxygenated blood to all the regions of the body.
Schematic diagram of blood circulation in humans
Therefore, the blood goes twice through the heart. This is known as double circulation. Importance of double circulation:
The separation of oxygenated and de-oxygenated blood allows a more efficient supply of oxygen to the body cells. This efficient system of oxygen supply is very useful in warm-blooded animals such as human beings.
As we know, warm-blooded animals have to maintain a constant body temperature by cooling themselves when they are in a hotter environment and by warming their bodies when they are in a cooler environment. Hence, they require more O2 for more respiration so that they can produce more energy to maintain their body temperature. Thus, the circulatory system of humans is more efficient because of the double circulatory heart.
Transport of materials in xylem | Transport of materials in phloem |
(i) Xylem tissue helps in the transport of water and minerals. | (i) Phloem tissue helps in the transport of food. |
(ii)Water is transported upwards from roots to all other plant parts. | (ii)Food is transported in both upward and downward directions. |
(iii)Transport in xylem occurs with the help of simple physical forces such as transpiration pull. | (iii)Transport of food in phloem requires energy in the form of ATP. |
Structure Structure
Alveoli are tiny balloon-like (i) Nephrons are tubular structures present inside the kidneys. structures present inside the lungs.
Nephrons are made of glomerulus, bowman’s capsule, and
The walls of the alveoli are one a long renal tube. It also contains a cluster of thin-walled cell thick and it contains an capillaries.
extensive network of blood capillaries.
Function
The exchange of O2 and Function
CO2 takes place between the blood of the capillaries that surround the (i) The blood enters the kidneys through the renal artery which alveoli and the gases present in the branches into many capillaries in the glomerulus. The water
alveoli. and solute are transferred to the nephron at Bowman’s
Nephrons are the basic filtr
NCERT Solutions for Class 10th: Ch 7 Control and Coordination Science In Text Questions
Page No: 119
What is the difference between a reflex action and walking?
A reflex action is voluntary action which is a rapid and automatic response to stimuli while walking is a voluntary action which requires our thinking and in our control.
What happens at the synapse between two neurons?
A synapse is the gap between the two neurons. At synapse the electrical signals converted into chemicals that can easily cross over the gap and pass on to the next neurons where it again converted into electrical signals.
Which part of the brain maintains posture and equilibrium of the body?
Cerebellum
How do we detect the smell of an agarbatti (incense stick)?
When the smell of the incense stick reaches to our nose then the olfactory receptors present in our nose detects it send this information in fore brain in the form of electrical signals. Fore brain interprets this information as the smell of incense stick where it is already stored.
What is the role of the brain in reflex action?
Brain has no direct involvement in reflex action. It is mainly controlled by Spinal Cord as these action not requires thinking and are very quick action.
Page No: 122
What are plant hormones?
Plant hormones are the fluids which are secreted within the plant also known as phytohormones. Plant hormones regulate the growth and development of the plant. Examples of plant hormones are auxin, gibberellins etc.
How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
The movements of the leaves of the sensitive plant are touch sensitive and independent of growth while the movement of the shoot towards light is growth related and known as phototropism.
Give an example of a plant hormone that promotes growth.
Auxin
How do auxins promote the growth of a tendril around a support?
When tendrils come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This is caused by the action of auxin hormone. Less auxin occurs on the side of contact as compared to the free side as a result, auxin promotes growth on the free side and the tendrils coil around the support.
Design an experiment to demonstrate hydrotropism.
Take two small beakers and label them as A and B. Fill beaker A with water. Now make a cylindrical-shaped roll from a filter paper and keep it as a bridge between beaker A and beaker B, as shown in the figure. Attach few germinating seeds in the middle of the filter paper bridge. Now, cover the entire set-up with a transparent plastic container so that the moisture is retained.
Observation:
The roots of the germinating seeds will grow towards beaker A.
This experiment demonstrates the phenomenon of hydrotropism. Page No: 125
How does chemical coordination take place in animals?
Chemical coordination takes place in animals with the help of hormones. Hormones are the chemical fluids that are secreted by the glands of the endocrine system. Hormones regulate the overall growth and development of the animals.
Why is the use of iodised salt advisable?
Iodine stimulates the thyroid gland to produce thyroxin hormone. It regulates carbohydrate, fat, and protein metabolism in our body. Deficiency of this
hormone results in the enlargement of the thyroid gland. This can lead to goitre, a disease characterized by swollen neck. Therefore, iodised salt is advised for normal functioning of the thyroid gland.
How does our body respond when adrenaline is secreted into the blood?
When someone is in danger or in emergency then adrenal gland secrete adrenaline hormone. It is secreted directly into the blood and is transported to different parts of the body. It speeds up the heartbeat and hence supplies more oxygen to the muscles. This results in increasing breathing rate and blood pressure which enable them to fight with such urgent situation.
Why are some patients of diabetes treated by giving injections of insulin?
Diabetes is caused due to less or no secretion of hormone insulin by pancreas. In such a person, blood sugar level is high. Insulin converts extra sugar present in blood into glycogen. Thus, patients suffering from diabetes are given insulin injection to control their blood sugar level.
Excercise
Which of the following is a plant hormone?
Insulin
Thyroxin
Oestrogen
Cytokinin
(d) Cytokinin
The gap between two neurons is called a
dendrite.
synapse.
axon.
impulse.
(b) synapse.
Page No: 126
The brain is responsible for
thinking.
regulating the heart beat.
balancing the body.
all of the above.
(d) all of the above.
What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Functions of receptors:
→ They sense the external stimuli such as heat or pain.
→ They also trigger an impulse in the sensory neuron which sends message to the spinal cord.
When the receptors are damaged, the external stimuli transferring signals to the brain are not felt. For example, in the case of damaged receptors, if we accidentally touch any hot object, then our hands might get burnt as damaged receptors cannot perceive the external stimuli of heat and pain.
Draw the structure of a neuron and explain its function.
Functions of the three parts of a neuron:
→ Axon: It conducts messages away from the cell body.
→ Dendrite: It receives information from axon of another cell and conducts the messages towards the cell body.
→ Cell body: It contains nucleus, mitochondria, and other organelles. It is mainly concerned with the maintenance and growth.
How does phototropism occur in plants?
The growth movement in plants in response to light stimulus is known as phototropism.The shoots show positive phototropism and the roots show negative phototropism. This means that the shoots bend towards the source of light whereas the roots bend away from the light source.
For Example: The flower head of sunflower is positively phototropic and hence it moves from east to west along with the sun.
Which signals will get disrupted in case of a spinal cord injury?
In case of the spinal cord injury, the signals coming from the nerves as well as the signals coming to the receptors will be disrupted. As both these signals meet in a bundle in spinal cord so there is any spinal cord injury then both these signals are disrupted.
How does chemical coordination occur in plants?
Chemical coordination occurs in plants with the help of plant hormones. Different plant hormones help to coordinate growth, development, and responses to the environment. They are synthesized at places away from where they act and diffuse to the area for action, For example, auxin promotes cell growth, gibberellins promote stem growth, cytokinins promote cell division and abscisic acid inhibits growth and its effects include wilting of leaves.
What is the need for a system of control and coordination in an organism?
There are various organs in an organism. These organs must be carefully controlled and coordinated for the survival of an organisms. In the body of an organism various fluids are secreted from the glands of the endocrine system. These hormones are responsible for the overall growth and development of an organism. All others daily decision that includes voluntary and involuntary action are controlled by central nervous system(CNS).
How are involuntary actions and reflex actions different from each other?
Involuntary action is the set of muscle movement which do not require thinking. But it is controlled by brain for example beating of heart beat while on the other hand, the reflex action is rapid and spontaneous action in response to any stimulus. For example closing of eyes immediately when bright light is focused.
Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Nervous System Mechanism | Hormonal System Mechanism |
It is consist of nerve impulses between PNS, CNS and Brain. | It consists of endocrine system which secretes hormones directly into blood. |
The axons and dendrites transmit the information through a coordinated effort. | The information is transmitted or transported through blood. |
The flow of information is rapid and the response is quick. | The information travels slowly and the response is slow. |
Nerve impulses are not specific in their action. | Each hormone has specific actions. |
Effects are short lived. | It has prolonged effects. |
What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
Movement in sensitive plants | Movement in our legs |
The movement in a sensitive plant is a response to stimulus(touch) which is a involuntary action. | Movement in our legs is a voluntary action. |
No special tissue is there for the transfer of information | A complete system CNS and PNS is there for the information exchange. |
Plant cells do not have specialised protein for movements. | Animal cells have specialised protein which help muscles to contract. |
Thus, it is the DNA molecule that determines the body design of an individual. Therefore, it can be concluded that it is the DNA that gets transferred from parents to offsprings and makes them look similar.
DNA determines body structure
Binary fission in Amoeba
In multiple fission, a single cell divides into many daughter cells simultaneously. Amoeba andPlasmodium divide by multiple fission.
Multiple fission in Plasmodium
Large numbers of spores are produced in one sporangium.
Spores are distributed easily by air to far-off places to avoid competition at one place.
Spores are covered by thick walls to prevent dehydration under unfavourable conditions.
However, complex organisms have organ-system level of organization. All the organ systems of their body work together as an interconnected unit. They can regenerate their lost body parts such as skin, muscles, blood, etc. However, they cannot give rise to new individuals through regeneration.
copies of DNA. The copying of DNA always takes place along with the creation of additional cellular structure. This process is then followed by division of a cell to form two cells.
Fertilization, on the other hand, is the fusion of the male and female gametes. It occurs inside the ovule and leads to the formation of zygote.
Increase in breast size and darkening of skin of the nipples present at the tips of the breasts.
Appearance of hair in the genital area.
Appearance of hair in other areas of skin like underarms, face, hands, and legs.
Increase in the size of uterus and ovary.
Beginning of menstrual cycle.
More secretion of oil from the skin, which results in the appearance of pimples.
amoeba.
yeast.
plasmodium.
leishmania.
Ovary
Uterus
Vas deferens
Fallopian tube
sepals.
ovules.
carpel.
pollen grains.
In sexual reproduction, more variations are produced. Thus, it ensures survival of species in a population.
The new formed individual has characteristics of both the parents.
Variations are more viable in sexual mode than in asexual one. This is because in asexual reproduction, DNA has to function inside the inherited cellular apparatus.
Functions of testes:
Produce sperms
Produce a hormone called testosterone, which brings about secondary sexual characters in boys.
Oral contraceptives →In this method, tablets or drugs are taken orally. These contain small doses of hormones that prevent the release of eggs and thus fertilization cannot occur.
Implants and surgical methods →Contraceptive devices such as the loop or Copper-T are placed in uterus to prevent pregnancy. Some surgical methods can also be used to block the gamete transfer. It includes the blocking of vas deferens to prevent the transfer of sperms known as vasectomy. Similarly, fallopian tubes of the female can be blocked so that the egg will not reach the uterus known as tubectomy.
Therefore, reproduction provides stability to populations of dogs or cats or any other species.
To prevent unwanted pregnancies.
To control population rise or birth rate.
To prevent the transfer of sexually transmitted diseases.
It can be easily observed in the above figure that in asexual reproduction, very few variations are allowed. Therefore, if a trait is present in only 10% of the population, it is more likely that the trait has arisen recently. Hence, it can be concluded that trait B that exists in 60% of the same population has arisen earlier than trait A.
However, not all variations are useful. Therefore, these are not necessarily beneficial for the individual organisms.
Cross-pollination of tall and short plant
Then, Mendel self-pollinated the F1 plants and observed that all plants obtained in the F2 generation were not tall. Instead, one-fourth of the F2 plants were short.
Self-pollination of F1 plants
From this experiment, Mendel concluded that the F1 tall plants were not true breeding. They were carrying traits of both short height and tall height. They appeared tall only because the tall trait is dominant over the dwarf trait.
An example of dihybrid crosses
Since the F1 plants are formed after crossing pea plants having green round seeds and pea plants having yellow wrinkled seeds, F1 generation will have both these characters in them. However, as we know that yellow seed colour and round seeds are dominant characters, therefore, the F1 plants will have yellow round seeds.
Then this F1 progeny was self-pollinated and the F2 progeny was found to have yellow round seeds, green round seeds, yellow wrinkled seeds, and green wrinkled seeds in the ratio of 9:3:3:1.
Independent inheritance of two different traits
In the above cross, more than two factors are involved, and these are independently inherited.
− is dominant? Why or why not?
Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any such conclusion.
The gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes and either X or Y sex chromosome.
Type of male gametes: 22+X OR 22+ Y.
However, since the females have XX sex chromosomes, their gametes can only have X sex chromosome.
Type of female gamete: 22+ X
Sex determination in humans
Thus, the mother provides only X chromosomes. The sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.
Natural selection: When that trait offers some survival advantage.
Genetic drift: When some genes governing that trait become common in a population.
When that trait gets acquired during the individual’s lifetime.
Small numbers of tigers means that fewer variations in terms of genes are available. This means that when these tigers reproduce, there are less chances of producing progeny with some useful variations. Hence, it is a cause of worry from the point of view of genetics.
Therefore, bacteria, spiders, fish, and chimpanzees are all different branches of evolution.
TTWW
TTww
TtWW
TtWw
Since all the progeny bore violet flowers, it means that the tall plant having violet flowers has WW genotype for violet flower colour.
Since the progeny is both tall and short, the parent plant was not a pure tall plant. Its genotype must be Tt.
Therefore, the cross involved in the given question is TtWw×ttww
↓ TtWw−ttww
Therefore, half the progeny is tall, but all of them have violet flowers.
our arm and a dog’s fore-leg.
our teeth and an elephant’s tusks.
potato and runners of grass.
all of the above.
a Chinese school-boy.
a chimpanzee.
a spider.
a bacterium.
LL × LL
↓ LL
If the children with light-coloured eyes have ll genotype, then their parents will also have ll genotype.
ll×ll
↓ ll
Therefore, it cannot be concluded whether light eye colour is dominant or recessive.
Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have a more recent ancestor.
For example, in a family, a brother and sister are closely related and they have a recent common ancestor i.e., their parents. A brother and his cousin are also related but less than the sister and her brother. This is because the brother and his cousin have a common ancestor i.e., their grandparents in the second generation whereas the parents were from the first generation.
With subsequent generations, the variations make organisms more different than their ancestors.
This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree.
Homologous organs
Analogous organs, on the other hand, have different origin but perform similar functions. For example, the wings of a bird and a bat are similar in function but this similarity does not mean that these animals are more closely related. If we carefully look at these structures, then we will find that the wings of a bat are just the folds of skin that are stretched between its fingers whereas the wings of birds are present all along the arm. Therefore, these organs are analogous organs.
A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the B series, a dog can be genetically black or brown.
Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb)
bb BB
B B
bBbBb bBbBb
In this case, all the offsprings will be heterozygous (Bb).
Since black (B) is dominant, all the offsprings will be black. However, they will have both B and b alleles.
If such heterozygous pups are crossed, they will produce 25% homozygous black (BB), 50 % heterozygous black (Bb), and 25% homozygous brown (bb) offsprings.
B b BBBBb
bBbBb
Around 100 million years ago, some invertebrates died and were buried in the soil in that area. More sediment accumulated on top of it turning it into sedimentary rock.
At the same place, millions of years later, some dinosaurs died and their bodies were buried on top of the sedimentary rock. The mud containing dinosaurs also turned into a rock.
Then, millions of years later, some horse-like creatures died in that area and got fossilized in rocks above the dinosaur fossils.
Some time later, due to soil erosion or floods in that area, the rocks containing horse-like fossils are exposed.
If that area is excavated deeper, then the dinosaur and invertebrates fossils can also be found. Thus, by digging that area, scientists can easily predict that horse-like animals evolved later than the dinosaurs and the invertebrates.
Thus, the above example suggests that the fossils found closer to the surface of the earth are more recent ones than the fossils present in deeper layers.
Layers of fossils
After the formation of water, slowly the earth surface cooled and the inorganic molecules interacted with one another in water to form simple organic molecules such as sugars, fatty acids, amino acids, etc. The energy for these reactions was provided by solar radiations, lightning, volcanic eruptions, etc.
This was proved by the experiment of Stanley L. Miller and Harold C. Urey in 1953.
They took a mixture of water (H2O), methane (CH4), ammonia (NH3), and hydrogen gas (H2) in a chamber and sparks were passed through this mixture using two electrodes. After one week, 15
% of the carbon from methane was converted into amino acids, sugars, etc. These organic molecules are polymerized and assembled to form protein molecules that gave rise to life on earth.
Miller and Urey experiment
Additionally, asexual reproduction allows very less variations because if there are more variations, then the resultant DNA will not be able to survive inside the inherited cellular apparatus.
However, in sexual reproduction, more variations are allowed and the resultant DNA is also able to survive, thus making the variations viable.
Variation and Evolution: Variants help the species to survive in all the conditions. Environmental conditions such as heat, light, pests, and food availability can change suddenly at only one place. At that time, only those variants resistant to these conditions would be able to survive. This will slowly lead to the evolution of a better adapted species. Thus, variation helps in the evolution of sexually reproducing organisms.
Females have two X chromosomes and males have one X and one Y chromosome.
The gamete receives half of the chromosomes. Therefore, the male gametes have 22 autosomes and either X or Y chromosome.
The female gamete, on the other hand, has 22 autosomes and X chromosome.
During reproduction, the male and female gametes fuse and thus the progeny receives 22 autosomes and one X or Y chromosome from male parent and 22 autosomes and one X chromosome from the female parent.
However, there can be some other variations, which do not offer any survival advantage and arise only accidentally. Such variations in small populations can change the frequency of some genes even if they are not important for survival.
This accidental change in the frequency of genes in small populations is referred to as genetic drift.
Thus, genetic drift provides diversity (variations) without any survival advantage.
Radius of curvature of a spherical mirror = 2 × Focal length ( f ) R = 2 f
Hence, the focal length of the given spherical mirror is 10 cm.
Hence, the focal length of the given convex mirror is 16 cm.
Let the height of the object, ho = h
Then, height of the image, hI = −3h (Image formed is real)
Object distance, u = −10 cm v = 3 × (−10) = −30 cm
Here, the negative sign indicates that an inverted image is formed at a distance of 30 cm in front of the given concave mirror.
When a ray of light travels from an optically rarer medium to an optically denser medium, it gets bent towards the normal. Since water is optically denser than air, a ray of light travelling from air into the water will bend towards the normal.
Refractive index of a medium nm is given by,
Speed of light in vacuum, c = 3 × 108 m s−1 Refractive index of glass, ng = 1.50
Speed of light in the glass,
Material Refractive index Material medium Refractive
medium | index | ||
Air | 1.0003 | Canada Balsam | 1.53 |
Ice | 1.31 | - | - |
Water | 1.33 | Rock salt | 1.54 |
Alcohol | 1.36 | - | - |
Kerosene | 1.44 | Carbon disulphide | 1.63 |
Fused quartz | 1.46 | Dense flint glass | 1.65 |
Turpentine oil | 1.47 | Ruby | 1.71 |
Benzene Crown | 1.50 | Sapphire | 1.77 |
1.52 | Diamond | 2.42 | |
glass |
Optical density of a medium is directly related with the refractive index of that medium. A medium which has the highest refractive index will have the highest optical density and vice- versa.
It can be observed from table 10.3 that diamond and air respectively have the highest and lowest refractive index. Therefore, diamond has the highest optical density and air has the lowest optical density.
Material medium | Refractive indexMaterial medium Refractive | ||
index | |||
Air | 1.0003 | Canada Balsam | 1.53 |
Ice | 1.31 | - | - |
Water | 1.33 | Rock salt | 1.54 |
Alcohol | 1.36 | - | - |
Kerosene | 1.44 | Carbon disulphide | 1.63 |
Fused quartz | 1.46 | Dense flint glass | 1.65 |
Turpentine oil | 1.47 | Ruby | 1.71 |
Benzene Crown | 1.50 | Sapphire | 1.77 |
glass | 1.52 | Diamond | 2.42 |
It can be inferred from the relation that light will travel the slowest in the material which has the highest refractive index and travel the fastest in the material which has the lowest refractive index.
It can be observed from table 10.3 that the refractive indices of kerosene, turpentine, and water are 1.44, 1.47, and 1.33 respectively. Therefore, light travels the fastest in water.
Where, c is the speed of light in vacuum/air
The refractive index of diamond is 2.42. This suggests that the speed of light in diamond will reduce by a factor 2.42 compared to its speed in air.
The S.I. unit of power of a lens is Dioptre. It is denoted by D.
1 dioptre is defined as the power of a lens of focal length 1 metre.
1 D = 1 m−1
It is given that the image of the needle is formed at a distance of 50 cm from the convex lens. Hence, the needle is placed in front of the lens at a distance of
50 cm.
Object distance, u = −50 cm Image distance, v = 50 cm Focal length = f
According to the lens formula,
Hence, the power of the given lens is +4 D.
Here, negative sign arises due to the divergent nature of concave lens. Hence, the power of the given concave lens is −0.5 D.
Water
Glass
Plastic
Clay
Between the principal focus and the centre of curvature
At the centre of curvature
Beyond the centre of curvature
Between the pole of the mirror and its principal focus
At the principal focus of the lens
At twice the focal length
At infinity
Between the optical centre of the lens and its principal focus.
both concave
both convex
the mirror is concave and the lens is convex
the mirror is convex, but the lens is concave
plane
concave
convex
either plane or convex
A convex lens of focal length 50 cm
A concave lens of focal length 50 cm
A convex lens of focal length 5 cm
A concave lens of focal length 5 cm
A concave mirror gives an erect image when an object is placed between its pole (P) and the principal focus (F).
Hence, to obtain an erect image of an object from a concave mirror of focal length 15 cm, the object must be placed anywhere between the pole and the focus. The image formed will be virtual, erect, and magnified in nature, as shown in the given figure.
Headlights of a car
Side/rear-view mirror of a vehicle
Solar furnace
Support your answer with reason.
Concave mirror is used in the headlights of a car. This is because concave mirrors can produce powerful parallel beam of light when the light source is placed at their principal focus.
Convex mirror is used in side/rear view mirror of a vehicle. Convex mirrors give a virtual, erect, and diminished image of the objects placed in front of it. Because of this, they have a wide field of view. It enables the driver to see most of the traffic behind him/her.
Concave mirrors are convergent mirrors. That is why they are used to construct solar furnaces. Concave mirrors converge the light incident on them at a single point known as principal focus. Hence, they can be used to produce a large amount of heat at that point.
Case I
When the upper half of the lens is covered
In this case, a ray of light coming from the object will be refracted by the lower half of the lens. These rays meet at the other side of the lens to form the image of the given object, as shown in the following figure.
Case II
When the lower half of the lens is covered
In this case, a ray of light coming from the object is refracted by the upper half of the lens. These rays meet at the other side of the lens to form the image of the given object, as shown in the following figure.
Focal length, f = +10 cm
According to the lens formula,
The positive value of v shows that the image is formed at the other side of the lens.
The negative sign shows that the image is real and formed behind the lens.
The negative value of image height indicates that the image formed is inverted. The position, size, and nature of image are shown in the following ray diagram.
According to the lens formula,
The negative value of u indicates that the object is placed 30 cm in front of the lens. This is shown in the following ray diagram.
According to the mirror formula,
The positive value of v indicates that the image is formed behind the mirror.
The positive value of magnification indicates that the image formed is virtual and erect. The magnification produced by a plane mirror is +1. What does this mean?
Magnification produced by a mirror is given by the relation
The magnification produced by a plane mirror is +1. It shows that the image formed by the plane mirror is of the same size as that of the object. The positive sign shows that the image formed is virtual and erect.
Radius of curvature, R = 30 cm Radius of curvature = 2 × Focal length R = 2 f
f = 15 cm
According to the mirror formula,
The positive value of v indicates that the image is formed behind the mirror.
The positive value of image height indicates that the image formed is erect. Therefore, the image formed is virtual, erect, and smaller in size.
Focal length, f = −18 cm According to the mirror formula,
The screen should be placed at a distance of 54 cm in front of the given mirror.
The negative value of magnification indicates that the image formed is real.
The negative value of image height indicates that the image formed is inverted.
A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
The person is able to see nearby objects clearly, but he is unable to see objects beyond 1.2 m. This happens because the image of an object beyond 1.2 m is formed in front of the retina and not at the retina, as shown in the given figure.
To correct this defect of vision, he must use a concave lens. The concave lens will bring the image back to the retina as shown in the given figure.
The far point of the eye is the maximum distance to which the eye can see the objects clearly. The far point of the normal human eye is infinity.
presbyopia
accommodation
near-sightedness
far-sightedness
(a) cornea (b) iris (c) pupil (d) retina
25 m
2.5 cm
25 cm
2.5 m
Power of the lens used for correcting distant vision = −5.5 D
Focal length of the required lens, f =
The focal length of the lens for correcting distant vision is −0.181 m.
Power of the lens used for correcting near vision = +1.5 D Focal length of the required lens, f = 
The focal length of the lens for correcting near vision is 0.667 m.
Object distance, u = infinity =
Image distance, v = −80 cm Focal length = f
According to the lens formula,
We know,
A concave lens of power −1.25 D is required by the person to correct his defect.
Object distance, u = infinity =
Image distance, v = −80 cm Focal length = f
According to the lens formula,
We know,
A concave lens of power −1.25 D is required by the person to correct his defect.
The convex lens actually creates a virtual image of a nearby object (N’ in the figure) at the near point of vision (N) of the person suffering from hypermetropia.
The given person will be able to clearly see the object kept at 25 cm (near point of the normal eye), if the image of the object is formed at his near point, which is given as 1 m.
Object distance, u = −25 cm
Image distance, v = −1 m = −100 m Focal length, f
Using the lens formula,
A convex lens of power +3.0 D is required to correct the defect.
If the object is placed at a distance less than 25 cm from the eye, then the object appears blurred and produces strain in the eyes.
NCERT Solutions for Class 10th: Ch 12 Electricity Science In Text Questions
Page No: 200
What does an electric circuit mean?
Answer
A continuous and closed path of an electric current is called an electric circuit. An electric circuit consists of electric devices, source of electricity and wires that are connected with the help of a switch.
Define the unit of current.
Answer
The unit of electric current is ampere (A). 1 A is defined as the flow of 1 C of charge through a wire in 1 s.
Calculate the number of electrons constituting one coulomb of charge.
Answer
One electron possesses a charge of 1.6 ×10-19C, i.e., 1.6 ×10-19C of charge is contained in 1 electron.
∴ 1 C of charge is contained in 1/1.6 x 10-19 = 6.25 x 1018 = 6 x 1018 Therefore, 6 x 1018 electrons constitute one coulomb of charge.
Page No: 202
Name a device that helps to maintain a potential difference across a conductor.
Answer
Any source of electricity like battery, cell, power supply, etc. helps to maintain a potential difference across a conductor.
What is meant by saying that the potential difference between two points is 1 V?
Answer
If 1 J of work is required to move a charge of amount 1 C from one point to another, then it is
said that the potential difference between the two points is 1 V.
How much energy is given to each coulomb of charge passing through a 6 V battery?
Answer
The energy given to each coulomb of charge is equal to the amount of work which is done in moving it.
Now we know that,
Potential difference = Work Done/Charge
∴ Work done = Potential difference × charge Where, Charge = 1 C and Potential difference = 6 V
∴ Work done = 6×1
= 6 Joule.
Page No: 209
On what factors does the resistance of a conductor depend?
Answer
The resistance of a conductor depends upon the following factors:
→ Length of the conductor
→ Cross-sectional area of the conductor
→ Material of the conductor
→ Temperature of the conductor
Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?
Answer
The current will flow more easily through thick wire. It is because the resistance of a conductor is inversely proportional to its area of cross - section. If thicker the wire, less is resistance and hence more easily the current flows.
Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?
Answer
According to Ohm’s law
V = IR
⇒ I=V/R ... (1)
Now Potential difference is decreased to half
∴ New potential difference Vʹ=V/2 Resistance remains constant
So the new current Iʹ = Vʹ/R
= (V/2)/R
= (1/2) (V/R)
= (1/2) I = I/2
Therefore, the amount of current flowing through the electrical component is reduced by half.
Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Answer
The resistivity of an alloy is higher than the pure metal. Moreover, at high temperatures, the alloys do not melt readily. Hence, the coils of heating appliances such as electric toasters and electric irons are made of an alloy rather than a pure metal.
Use the data in Table 12.2 to answer the following - Table 12.2 Electrical resistivity of some substances at 20°C
− | Material | Resistivity (Ω m) |
Conductors | Silver | 1.60 × 10−8 |
Copper | 1.62 × 10−8 | |
Aluminium | 2.63 × 10−8 | |
Tungsten | 5.20 × 10−8 | |
Nickel | 6.84 × 10−8 | |
Iron | 10.0 × 10−8 | |
Chromium | 12.9 × 10−8 | |
Mercury | 94.0 × 10−8 | |
Manganese | 1.84 × 10−6 | |
Constantan (alloy of Cu and Ni) | 49 × 10−6 |
Alloys | Manganin (alloy of Cu, Mn and Ni) | 44 × 10−6 |
Nichrome (alloy of Ni, Cr, Mn and Fe) | 100 × 10−6 | |
Glass | 1010 − 1014 | |
Insulators | Hard rubber | 1013 − 1016 |
Ebonite | 1015 − 1017 | |
Diamond | 1012 − 1013 | |
Paper (dry) | 1012 |
Answer
Resistivity of iron = 10.0 x 10-8 Ω Resistivity of mercury = 94.0 x 10-8 Ω
Resistivity of mercury is more than that of iron. This implies that iron is a better conductor than mercury.
It can be observed from Table 12.2 that the resistivity of silver is the lowest among the listed materials. Hence, it is the best conductor.
Page No: 213
Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a 5 Ω resistor, an 8 Ω resistor, and a 12 Ω resistor, and a plug key, all connected in series.
Answer
Three cells of potential 2 V, each connected in series therefore the potential difference of the battery will be 2 V + 2 V + 2 V = 6V. The following circuit diagram shows three resistors of
resistances 5 Ω, 8 Ω and 12 Ω respectively connected in series and a battery of potential 6 V and a plug key which is closed means the current is flowing in the circuit.
Redraw the circuit of question 1, putting in an ammeter to measure the current through the resistors and a voltmeter to measure potential difference across the 12 Ω resistor. What would be the readings in the ammeter and the voltmeter?
Answer
An ammeter should be connected in the circuit in series with the resistors. To measure the potential difference across the resistor it should be connected in parallel, as shown in the following figure.
The resistances are connected in series.
Ohm’s law can be used to obtain the readings of ammeter and voltmeter. According to Ohm’s law,
V = IR,
Where,
Potential difference, V = 6 V
Current flowing through the circuit/resistors = I
Resistance of the circuit, R = 5 + 8 + 12 = 25Ω
I = V/R = 6/25 = 0.24 A
Potential difference across 12 Ω resistor = V1
Current flowing through the 12 Ω resistor, I = 0.24 A Therefore, using Ohm’s law, we obtain
V1 = IR = 0.24 x 12 = 2.88 V
Therefore, the reading of the ammeter will be 0.24 A. The reading of the voltmeter will be 2.88 V.
Page No: 216
Judge the equivalent resistance when the following are connected in parallel − (a) 1 Ω and 106Ω, (b) 1 Ω and 103Ω and 106Ω.
Answer
An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filter of resistance 500 Ω are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current
through it?
Answer
Resistance of electric lamp, R1 = 100 Ω Resistance of toaster, R2 = 50 Ω Resistance of water filter, R3 = 500 Ω
Potential difference of the source, V = 220 V
These are connected in parallel, as shown in the following figure.
Let R be the equivalent resistance of the circuit.
What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
Answer
There is no division of voltage among the appliances when connected in parallel. The potential difference across each appliance is equal to the supplied voltage.
The total effective resistance of the circuit can be reduced by connecting electrical appliances in parallel.
How can three resistors of resistances 2 Ω, 3 Ω and 6 Ω be connected to give a total resistance of (a) 4 Ω, (b) 1 Ω?
Answer
There are three resistors of resistances 2 Ω, 3 Ω, and 6 Ω respectively.
The following circuit diagram shows the connection of the three resistors.
Here, 6 Ω and 3 Ω resistors are connected in parallel. Therefore, their equivalent resistance will be given by
This equivalent resistor of resistance 2 Ω is connected to a 2 Ω resistor in series. Therefore, the equivalent resistance of the circuit = 2 Ω + 2 Ω = 4 Ω
Hence the total resistance of the circuit is 4 Ω.
The following circuit diagram shows the connection of the three resistors.
All the resistors are connected in series. Therefore, their equivalent resistance will be given as
Therefore, the total resistance of the circuit is 1 Ω.
What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω?
Answer
There are four coils of resistances 4 Ω, 8 Ω, 12 Ω and 24 Ω respectively.
If these coils are connected in series, then the equivalent resistance will be the highest, given by the sum 4 + 8 + 12 + 24 = 48 Ω
If these coils are connected in parallel, then the equivalent resistance will be the lowest, given by
Therefore, 2 Ω is the lowest total resistance. Page No: 218
Why does the cord of an electric heater not glow while the heating element does?
Answer
The heating element of the heater is made up of alloy which has very high resistance so when current flows through the heating element, it becomes too hot and glows red. But the resistance of cord which is usually of copper or aluminium is very law so it does not glow.
Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V.
Answer
Given Charge, Q = 96000C Time, t= 1hr = 60 x 60= 3600s Potential difference, V= 50volts Now we know that H= VIt
So we have to calculate I first As I= Q/t
∴ I = 96000/3600 = 80/3 A
Therefore, the heat generated is 4.8 x 106 J.
An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.
Answer
The amount of heat (H) produced is given by the joule's law of heating asH= Vlt Where,
Current, I = 5 A Time, t = 30 s
Voltage, V = Current x Resistance = 5 x 20 = 100 V H= 100 x 5 x 30 = 1.5 x 104 J.
Therefore, the amount of heat developed in the electric iron is 1.5 x 104 J. Page No: 220
What determines the rate at which energy is delivered by a current?
Answer
The rate of consumption of electric energy in an electric appliance is called electric power. Hence, the rate at which energy is delivered by a current is the power of the appliance.
An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h.
Answer
Power (P) is given by the expression,P = VI
Where,
Voltage,V = 220 V Current, I = 5 A
P= 220 x 5 = 1100 W
Energy consumed by the motor = Pt Where,
Time, t = 2 h = 2 x 60 x 60 = 7200 s
∴ P = 1100 x 7200 = 7.92 x 106 J
Therefore, power of the motor = 1100 W Energy consumed by the motor = 7.92 x 106 J
Page No: 221
Excercise
A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R', then the ratio R/R' is -(a) 1/25
(b) 1/5
(c) 5
(d) 25
(d) 25
Which of the following terms does not represent electrical power in a circuit?
I2R
IR2
VI
V2/R
(b) IR2
An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be -
100 W
75 W
50 W
25 W
(d) 25 W
Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be -
1:2
2:1
1:4
4:1
(c) 1:4
How is a voltmeter connected in the circuit to measure the potential difference between two points?
Answer
To measure the potential difference between two points, a voltmeter should be connected in parallel to the points.
A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10−8 Ω m. What will be the length of this wire to make its resistance 10 Ω? How much does the resistance change if the diameter is doubled?
Answer
Area of cross-section of the wire, A =π (d/2) 2 Diameter= 0.5 mm = 0.0005 m
Resistance, R = 10 Ω We know that
Therefore, the length of the wire is 122.7 m and the new resistance is 2.5 Ω.
The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below −
I (amperes ) | 0.5 | 1.0 | 2.0 | 3.0 | 4.0 |
V (volts) | 1.6 | 3.4 | 6.7 | 10.2 | 13.2 |
Plot a graph between V and I and calculate the resistance of that resistor.
Answer
The plot between voltage and current is called IV characteristic. The voltage is plotted on x-axis and current is plotted on y-axis. The values of the current for different values of the voltage are shown in the given table.
V (volts) | 1.6 | 3.4 | 6.7 | 10.2 | 13.2 |
I (amperes ) | 0.5 | 1.0 | 2.0 | 3.0 | 4.0 |
The IV characteristic of the given resistor is plotted in the following figure.
The slope of the line gives the value of resistance (R) as, Slope = 1/R = BC/AC = 2/6.8
R= 6.8/2 = 3.4 Ω
Therefore, the resistance of the resistor is 3.4 Ω.
When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.
Answer
Resistance (R) of a resistor is given by Ohm's law as,V= IR R= V/I
Where,
Potential difference, V= 12 V
Current in the circuit, I= 2.5 mA = 2.5 x 10-3 A
Therefore, the resistance of the resistor is 4.8 kΩ
A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?
Answer
There is no current division occurring in a series circuit. Current flow through the component is the same, given by Ohm’s law as
V= IR I= V/R
Where,
R is the equivalent resistance of resistances 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω. These are connected in series. Hence, the sum of the resistances will give the value of R.
R= 0.2 + 0.3 + 0.4 + 0.5 + 12 = 13.4 Ω
Potential difference, V= 9 V I= 9/13.4 = 0.671 A
Therefore, the current that would flow through the 12 Ω resistor is 0.671 A.
How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?
Answer
For x number of resistors of resistance 176 Ω, the equivalent resistance of the resistors connected in parallel is given by Ohm's law asV= IR
R= V/I
Where,
Supply voltage, V= 220 V
Current, I = 5 A
Equivalent resistance of the combination = R,given as
Therefore, four resistors of 176 Ω are required to draw the given amount of current.
Show how you would connect three resistors, each of resistance 6 Ω, so that the combination has a resistance of (i) 9 Ω, (ii) 4 Ω.
Answer
If we connect the resistors in series, then the equivalent resistance will be the sum of the
resistors, i.e., 6 Ω + 6 Ω + 6 Ω = 18 Ω, which is not desired. If we connect the resistors in parallel, then the equivalent resistance will be 6/2 = 3 Ω is also not desired. Hence, we should either connect the two resistors in series or parallel.
Two resistor in parallel
Two 6 Ω resistors are connected in parallel. Their equivalent resistance will be
The third 6 Ω resistor is in series with 3 Ω. Hence, the equivalent resistance of the circuit is 6 Ω+ 3 Ω = 9 Ω.
Two resistor in series
Two 6 Ω resistors are in series. Their equivalent resistance will be the sum 6 + 6 = 12 Ω. The third 6 Ω resistor is in parallel with 12 Ω. Hence, equivalent resistance will be
Therefore, the total resistance is 4 Ω.
Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A?
Answer
Resistance R1 of the bulb is given by the expression, Supply voltage, V = 220 V
Maximum allowable current, I = 5 A Rating of an electric bulb P=10watts Because R=V2/P
∴ Number of electric bulbs connected in parallel are 110.
A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B,
each of 24 Ω resistances, which may be used separately, in series, or in parallel. What are the currents in the three cases?
Answer
Supply voltage, V= 220 V
Resistance of one coil, R= 24 Ω
Coils are used separately According to Ohm's law, V= I1R1
Where,
I1 is the current flowing through the coil I1 = V/R1 = 220/24 = 9.166 A
Therefore, 9.16 A current will flow through the coil when used separately.
Coils are connected in series
Total resistance, R2 = 24 Ω + 24 Ω = 48 Ω According to Ohm's law,V = I2R2
Where,
I2 is the current flowing through the series circuit
I2 = V/R2 = 220/48 = 4.58 A
Therefore, 4.58 A current will flow through the circuit when the coils are connected in series.
Coils are connected in parallel Total resistance, R3 is given as =
According to Ohm's law,
V= I3R3
Where,
I3 is the current flowing through the circuit I3 = V/R3 = 220/12 = 18.33 A
Therefore, 18.33 A current will flow through the circuit when coils are connected in parallel.
Compare the power used in the 2 Ω resistor in each of the following circuits: (i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and (ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors.
Answer
Potential difference, V = 6 V
1 Ω and 2 Ω resistors are connected in series. Therefore, equivalent resistance of the circuit, R = 1 + 2 = 3 Ω
According to Ohm’s law,
V = IR
Where,
I is the current through the circuit
I= 6/3 = 2 A
This current will flow through each component of the circuit because there is no division of current in series circuits. Hence, current flowing through the 2 Ω resistor is 2 A. Power is given by the expression,
P= (I)2R = (2)2 x 2 = 8 W
Potential difference, V = 4 V
12 Ω and 2 Ω resistors are connected in parallel. The voltage across each component of a parallel circuit remains the same. Hence, the voltage across 2 Ω resistor will be 4 V. Power consumed by 2 Ω resistor is given by
P= V2/R = 42/2 = 8 W
Therefore, the power used by 2 Ω resistor is 8 W.
Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?
Answer
Both the bulbs are connected in parallel. Therefore, potential difference across each of them will be 220 V, because no division of voltage occurs in a parallel circuit.
Current drawn by the bulb of rating 100 W is given by,Power = Voltage x Current Current = Power/Voltage = 60/220 A
Hence, current drawn from the line = 100/220 + 60/220 = 0.727 A
Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?
Answer
Energy consumed by an electrical appliance is given by the expression,H= Pt Where,
Power of the appliance = P
Time = t
Energy consumed by a TV set of power 250 W in 1 h = 250 ×3600 = 9 ×105 J Energy consumed by a toaster of power 1200 W in 10 minutes = 1200 ×600 Energy consumed by a toaster of power 1200 W in 10 minutes = 1200 ×600
= 7.2×105 J
Therefore, the energy consumed by a 250 W TV set in 1 h is more than the energy consumed by
a toaster of power 1200 W in 10 minutes.
An electric heater of resistance 8 Ω draws 15 A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater.
Answer
Rate of heat produced by a device is given by the expression for power as, P= I2R
Where,
Resistance of the electric heater, R= 8 Ω Current drawn, I = 15 A
P= (15)2 x 8 = 1800 J/s
Therefore, heat is produced by the heater at the rate of 1800 J/s.
Explain the following.
Why is the tungsten used almost exclusively for filament of electric lamps?
Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
Why is the series arrangement not used for domestic circuits?
How does the resistance of a wire vary with its area of cross-section?
Why are copper and aluminium wires usually employed for electricity transmission?
Answer
The melting point and of Tungsten is an alloy which has very high melting point and very high resistivity so does not burn easily at a high temperature.
The conductors of electric heating devices such as bread toasters and electric irons are made of alloy because resistivity of an alloy is more than that of metals which produces large amount of heat.
In series circuits voltage is divided. Each component of a series circuit receives a small voltage so the amount of current decreases and the device becomes hot and does not work properly. Hence, series arrangement is not used in domestic circuits.
Resistance (R) of a wire is inversely proportional to its area of cross-section (A), i.e. when area of cross section increases the resistance decreases or vice versa.
Copper and aluminium are good conductors of electricity also they have low resistivity. So they are usually used for electricity transmission.
Magnetic field lines emerge from the north pole.
They merge at the south pole.
The direction of field lines inside the magnet is from the south pole to the north pole.
Magnetic lines do not intersect with each other.
For downward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop. Similarly, for upward direction of current flowing in the circular loop, the direction of
magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop, as shown in the given figure.
The magnetic field lines inside a current-carrying long straight solenoid are uniform.
For downward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop. Similarly, for upward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop, as shown in the given figure.
The magnetic field in a given region is uniform. Draw a diagram to represent it.
The magnetic field lines inside a current-carrying long straight solenoid are uniform.
The magnetic field inside a long straight solenoid-carrying current
is zero
decreases as we move towards its end
increases as we move towards its end
is the same at all points
mass
speed
velocity
momentum
When a proton enters in a region of magnetic field, it experiences a magnetic force. As a result of the force, the path of the proton becomes circular. Hence, its velocity and momentum change.
If a coil is moved rapidly between the two poles of a horse-shoe magnet, then an electric current is induced in the coil.
If a magnet is moved relative to a coil, then an electric current is induced in the coil.
two revolutions(b) one revolution
half revolution (d) one-fourth revolution
When a rectangular coil of copper is rotated in a magnetic field, the direction of the induced current in the coil changes once in each half revolution. As a result, the direction of current in the coil remains the same.
Each circuit must be connected with an electric fuse. This prevents the flow of excessive current through the circuit. When the current passing through the wire exceeds the maximum limit of the fuse element, the fuse melts to stop the flow of current through that circuit, hence protecting the appliances connected to the circuit.
Earthing is a must to prevent electric shocks. Any leakage of current in an electric appliance is transferred to the ground and people using the appliance do not get the shock.
Where, Current = I
Power of the oven, P = 2 kW = 2000 W Voltage supplied, V = 220 V
Hence, the current drawn by the electric oven is 9.09 A, which exceeds the safe limit of the circuit. Fuse element of the electric fuse will melt and break the circuit.
Too many appliances should not be connected to a single socket.
Too many appliances should not be used at the same time.
Faulty appliances should not be connected in the circuit.
Fuse should be connected in the circuit.
The field consists of straight lines perpendicular to the wire
The field consists of straight lines parallel to the wire
The field consists of radial lines originating from the wire
The field consists of concentric circles centred on the wire
the process of charging a body
the process of generating magnetic field due to a current passing through a coil
producing induced current in a coil due to relative motion between a magnet and the coil
the process of rotating a coil of an electric motor
generator
galvanometer
ammeter
motor
AC generator has an electromagnet while a DC generator has permanent magnet.
DC generator will generate a higher voltage.
AC generator will generate a higher voltage.
AC generator has slip rings while the DC generator has a commutator.
reduces substantially
does not change
increases heavily
vary continuously
An electric motor converts mechanical energy into electrical energy.
An electric generator works on the principle of electromagnetic induction.
The field at the centre of a long circular coil carrying current will be parallel straight lines.
A wire with a green insulation is usually the live wire of an electric supply.
An electric motor converts electrical energy into mechanical energy.
True
A generator is an electric device that generates electricity by rotating a coil in a magnetic field. It works on the principle of electromagnetic induction.
True
A long circular coil is a long solenoid. The magnetic field lines inside the solenoid are parallel lines.
False
Live wire has red insulation cover, whereas earth wire has green insulation colour in the domestic circuits.
Current-carrying conductors
Permanent magnets
Electromagnets
In the above figure, when the north pole of a bar magnet is brought near the end connected to the negative terminal of the battery, the solenoid repels the bar magnet. Since like poles repel each other, the end connected to the negative terminal of the battery behaves as the north pole of the solenoid and the other end behaves as a south pole. Hence, one end of the solenoid behaves as a north pole and the other end behaves as a south pole.
from back wall to the front wall. The direction of magnetic force is rightward. Hence, using Fleming’s left hand rule, it can be concluded that the direction of magnetic field inside the chamber is downward.
It works on the principle of the magnetic effect of current. A current-carrying coil rotates in a magnetic field. The following figure shows a simple electric motor.
When a current is allowed to flow through the coil MNST by closing the switch, the coil starts rotating anti-clockwise. This happens because a downward force acts on length MN and at the same time, an upward force acts on length ST. As a result, the coil rotates anti-clockwise.
Current in the length MN flows from M to N and the magnetic field acts from left to right, normal to length MN. Therefore, according to Fleming’s left hand rule, a downward force acts on the length MN. Similarly, current in the length ST flows from S to T and the magnetic field acts from left to right, normal to the flow of current. Therefore, an upward force acts on the length ST. These two forces cause the coil to rotate anti-clockwise.
After half a rotation, the position of MN and ST interchange. The half-ring D comes in contact with brush A and half-ring C comes in contact with brush B. Hence, the direction of current in the coil MNST gets reversed.
The current flows through the coil in the direction TSNM. The reversal of current through the coil MNST repeats after each half rotation. As a result, the coil rotates unidirectional. The split rings help to reverse the direction of current in the circuit. These are called the commutator.
Water pumps
Electric fans
Electric mixers
Washing machines
When a bar magnet is pushed into a coil of insulated copper wire, a current is induced momentarily in the coil. As a result, the needle of the galvanometer deflects momentarily in a particular direction.
When the bar magnet is withdrawn from inside the coil of the insulated copper wire, a current is again induced momentarily in the coil in the opposite direction. As a result, the needle of the galvanometer deflects momentarily in the opposite direction.
When a bar magnet is held stationary inside the coil, no current will be induced in the coil. Hence, galvanometer will show no deflection.
coil B also changes. This change in magnetic field lines around coil B induces an electric current in it. This is called electromagnetic induction.
Fleming’s left hand rule
Fleming’s right hand rule
The principle of working of an electric generator is that when a loop is moved in a magnetic field, an electric current is induced in the coil. It generates electricity by rotating a coil in a magnetic field. The following figure shows a simple AC generator.
MNST → Rectangular coil A and B → Brushes
C and D → Two slip rings
X → Axle, G → Galvanometer
If axle Xis rotated clockwise, then the length MN moves upwards while length ST moves downwards. Since the lengths MN and ST are moving in a magnetic field, a current will be
induced in both of them due to electromagnetic induction. Length MN is moving upwards and the magnetic field acts from left to right. Hence, according to Fleming’s right hand rule, the direction of induced current will be from M to N. Similarly, the direction of induced current in the length ST will be from S to T.
The direction of current in the coil is MNST. Hence, the galvanometer shows a deflection in a particular direction. After half a rotation, length MN starts moving down whereas length ST starts moving upward. The direction of the induced current in the coil gets reversed as TSNM. As the direction of current gets reversed after each half rotation, the produced current is called an alternating current (AC).
To get a unidirectional current, instead of two slip rings, two split rings are used, as shown in the following figure.
In this arrangement, brush A always remains in contact with the length of the coil that is moving up whereas brush B always remains in contact with the length that is moving down. The split rings C and D act as a commutator.
The direction of current induced in the coil will be MNST for the first rotation and TSNM in the second half of the rotation. Hence, a unidirectional current is produced from the generator called DC generator. The current is called AC current.
When the insulation of live and neutral wires undergoes wear and tear and then touches each other, the current flowing in the circuit increases abruptly. Hence, a short circuit occurs.
The biodegradable substances such as tree leaves, plant parts, and kitchen wastes can be used as humus after composting. This will enhance the soil fertility.
The biodegradable substances mainly contain carbon. These substances after decomposition release that carbon back into the atmosphere.
They contaminate soil and water resources as they cannot be decomposed by micro-organisms.
These substances, when accidentally eaten by stray animals, can harm them and can even cause their death.
The producers form the first trophic level as they manufacture food. The primary consumers form the second trophic level, the secondary consumers form the third, and the tertiary consumers form the fourth trophic level.
Trophic levels:
Various trophic levels are connected through food chains. For example, in an aquatic food chain, phytoplanktons are the producers, zooplanktons are the primary consumers, and small fish is the secondary consumer and so on.
Aquatic food chain
Then, this free oxygen atom combines with an oxygen molecule to form ozone.
In recent years, the amount of ozone in the atmosphere is getting depleted.
This ozone depletion causes a greater amount of ultra violet radiation to enter earth’s atmosphere. This has an indirect effect on the ecosystem.(Ecosystem includes both the biological community and the non-living components of an area). It results in the death of many phytoplanktons, thereby affecting the process of photosynthesis. Plants utilise atmospheric CO2 to make their food. In the absence of plants, the levels of CO2 in the atmosphere will increase, which would in turn lead to an increase in global warming.
The depletion in the ozone layer also increases the frequency of infectious diseases as it suppresses the immune systems of both human beings and animals. The frequency of skin cancer also increases in human beings because of the direct exposure to ultraviolet radiations.
The problem of waste management can be solved by the following given measures:
Use separate bins (blue and green) for disposing non-biodegradable and biodegradable wastes.
Different garbage bins for disposing biodegradable waste and non-biodegradable waste
Reduce the usage of non-biodegradable products such as plastics.
Grass, flowers and leather
Grass, wood and plastic
Fruit-peels, cake and lime-juice
Cake, wood and grass
Grass, wheat and mango
Grass, goat and human
Goat, cow and elephant
Grass, fish and goat
Carrying cloth-bags to put purchases in while shopping
Switching off unnecessary lights and fans
Walking to school instead of getting your mother to drop you on her scooter
All of the above
For example, in a food chain, if all the plants are killed, then all the deer will die due to lack of food. If all the deer are dead, then soon the tigers will also die. Due to the death of these animals, the decomposer’s population will rise in that area.
This is just an example of one food chain. However, in nature, food chains are not isolated. They are interconnected in the form of food web. Therefore, killing all the plants of an area will not only affect the deer, it will also affect other herbivores such as goat, cattle, sheep, etc.
Now let us suppose that all the deer (herbivores) are killed in a region. This can lead to an increase in the number of producers. At the same time, there will be an increase in the number of other herbivores such as rabbits, goat, sheep, etc. due to less competition. This will also lead to the increase in population of only consumers of these increased herbivores. Thus, the balance in the ecosystem gets disturbed if any of its component organisms are removed.
DDT.
Biomagnifications
Since the non-biodegradable substances cannot be broken down, they get accumulated and thus contaminate the soil and the water resources.
These substances, when accidentally eaten by some stray animal, can harm them and can even cause their death.
These substances occupy more space in the landfills and require special disposal techniques.
These materials can accumulate in the environment and can also enter the food chain.
Diagram representing ozone hole Consequences of ozone depletion:
It causes skin darkening, skin cancer, ageing, and corneal cataracts in human beings.
It can result in the death of many phytoplankton’s that leads to increased global warming.
To limit the damage to the ozone layer, the release of CFCs into the atmosphere must be reduced. CFCs used as refrigerants and in fire extinguishers should be replaced with environmentally-safe alternatives. Also, the release of CFCs through industrial activities should be controlled.
